Message ID | 20200319141132.3127-1-josef@toxicpanda.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | btrfs: use nofs allocations for running delayed items | expand |
On Thu, Mar 19, 2020 at 10:11:32AM -0400, Josef Bacik wrote: > This is because we hold that delayed node's mutex while doing tree > operations. Fix this by just wrapping the searches in nofs. For the time being we have to do the explicit NOFS so in the code it's a bit awkward. The hint is a function that takes transaction as argument. I'm working on the scope NOFS (marked by the transaction start/end), it's intrusive, all over the code and there are some cases when I want to add assertions that turns out to be tricky for some functions.
On 3/19/20 10:34 AM, David Sterba wrote: > On Thu, Mar 19, 2020 at 10:11:32AM -0400, Josef Bacik wrote: >> This is because we hold that delayed node's mutex while doing tree >> operations. Fix this by just wrapping the searches in nofs. > > For the time being we have to do the explicit NOFS so in the code it's > a bit awkward. The hint is a function that takes transaction as > argument. > > I'm working on the scope NOFS (marked by the transaction start/end), it's > intrusive, all over the code and there are some cases when I want to add > assertions that turns out to be tricky for some functions. > That could be cleaner, do you want me to drop this and just add a if (trans) memalloc_nofs_save() memalloc_nofs_restore() in btrfs_search_slot? That'll catch all of these usages. I'm not married to any particular approach. Thanks, Josef
On Thu, Mar 19, 2020 at 10:51:15AM -0400, Josef Bacik wrote: > On 3/19/20 10:34 AM, David Sterba wrote: > > On Thu, Mar 19, 2020 at 10:11:32AM -0400, Josef Bacik wrote: > >> This is because we hold that delayed node's mutex while doing tree > >> operations. Fix this by just wrapping the searches in nofs. > > > > For the time being we have to do the explicit NOFS so in the code it's > > a bit awkward. The hint is a function that takes transaction as > > argument. > > > > I'm working on the scope NOFS (marked by the transaction start/end), it's > > intrusive, all over the code and there are some cases when I want to add > > assertions that turns out to be tricky for some functions. > > > > That could be cleaner, do you want me to drop this and just add a > > if (trans) > memalloc_nofs_save() > > memalloc_nofs_restore() > > in btrfs_search_slot? That'll catch all of these usages. I'm not married to > any particular approach. Thanks, Not all I think but I haven't looked closer. Maybe the search slot is used in majority of cases anyway. The outer scope between memalloc_nofs_save/memalloc_nofs_restored has been used so far and it's obvious where it starts and ends so even if it's not pretty let's use it for now.
On Thu, Mar 19, 2020 at 10:11:32AM -0400, Josef Bacik wrote:
[...]
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Added to misc-next, thanks.
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c index ee70584ddc45..14de5b72e57a 100644 --- a/fs/btrfs/delayed-inode.c +++ b/fs/btrfs/delayed-inode.c @@ -6,6 +6,7 @@ #include <linux/slab.h> #include <linux/iversion.h> +#include <linux/sched/mm.h> #include "misc.h" #include "delayed-inode.h" #include "disk-io.h" @@ -805,11 +806,14 @@ static int btrfs_insert_delayed_item(struct btrfs_trans_handle *trans, struct btrfs_delayed_item *delayed_item) { struct extent_buffer *leaf; + unsigned int nofs_flag; char *ptr; int ret; + nofs_flag = memalloc_nofs_save(); ret = btrfs_insert_empty_item(trans, root, path, &delayed_item->key, delayed_item->data_len); + memalloc_nofs_restore(nofs_flag); if (ret < 0 && ret != -EEXIST) return ret; @@ -937,6 +941,7 @@ static int btrfs_delete_delayed_items(struct btrfs_trans_handle *trans, struct btrfs_delayed_node *node) { struct btrfs_delayed_item *curr, *prev; + unsigned int nofs_flag; int ret = 0; do_again: @@ -945,7 +950,9 @@ static int btrfs_delete_delayed_items(struct btrfs_trans_handle *trans, if (!curr) goto delete_fail; + nofs_flag = memalloc_nofs_save(); ret = btrfs_search_slot(trans, root, &curr->key, path, -1, 1); + memalloc_nofs_restore(nofs_flag); if (ret < 0) goto delete_fail; else if (ret > 0) { @@ -1012,6 +1019,7 @@ static int __btrfs_update_delayed_inode(struct btrfs_trans_handle *trans, struct btrfs_key key; struct btrfs_inode_item *inode_item; struct extent_buffer *leaf; + unsigned int nofs_flag; int mod; int ret; @@ -1024,7 +1032,9 @@ static int __btrfs_update_delayed_inode(struct btrfs_trans_handle *trans, else mod = 1; + nofs_flag = memalloc_nofs_save(); ret = btrfs_lookup_inode(trans, root, path, &key, mod); + memalloc_nofs_restore(nofs_flag); if (ret > 0) { btrfs_release_path(path); return -ENOENT; @@ -1075,7 +1085,10 @@ static int __btrfs_update_delayed_inode(struct btrfs_trans_handle *trans, key.type = BTRFS_INODE_EXTREF_KEY; key.offset = -1; + + nofs_flag = memalloc_nofs_save(); ret = btrfs_search_slot(trans, root, &key, path, -1, 1); + memalloc_nofs_restore(nofs_flag); if (ret < 0) goto err_out; ASSERT(ret);
Zygo reported the following lockdep splat while testing the balance patches ====================================================== WARNING: possible circular locking dependency detected 5.6.0-c6f0579d496a+ #53 Not tainted ------------------------------------------------------ kswapd0/1133 is trying to acquire lock: ffff888092f622c0 (&delayed_node->mutex){+.+.}, at: __btrfs_release_delayed_node+0x7c/0x5b0 but task is already holding lock: ffffffff8fc5f860 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x5/0x30 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (fs_reclaim){+.+.}: fs_reclaim_acquire.part.91+0x29/0x30 fs_reclaim_acquire+0x19/0x20 kmem_cache_alloc_trace+0x32/0x740 add_block_entry+0x45/0x260 btrfs_ref_tree_mod+0x6e2/0x8b0 btrfs_alloc_tree_block+0x789/0x880 alloc_tree_block_no_bg_flush+0xc6/0xf0 __btrfs_cow_block+0x270/0x940 btrfs_cow_block+0x1ba/0x3a0 btrfs_search_slot+0x999/0x1030 btrfs_insert_empty_items+0x81/0xe0 btrfs_insert_delayed_items+0x128/0x7d0 __btrfs_run_delayed_items+0xf4/0x2a0 btrfs_run_delayed_items+0x13/0x20 btrfs_commit_transaction+0x5cc/0x1390 insert_balance_item.isra.39+0x6b2/0x6e0 btrfs_balance+0x72d/0x18d0 btrfs_ioctl_balance+0x3de/0x4c0 btrfs_ioctl+0x30ab/0x44a0 ksys_ioctl+0xa1/0xe0 __x64_sys_ioctl+0x43/0x50 do_syscall_64+0x77/0x2c0 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #0 (&delayed_node->mutex){+.+.}: __lock_acquire+0x197e/0x2550 lock_acquire+0x103/0x220 __mutex_lock+0x13d/0xce0 mutex_lock_nested+0x1b/0x20 __btrfs_release_delayed_node+0x7c/0x5b0 btrfs_remove_delayed_node+0x49/0x50 btrfs_evict_inode+0x6fc/0x900 evict+0x19a/0x2c0 dispose_list+0xa0/0xe0 prune_icache_sb+0xbd/0xf0 super_cache_scan+0x1b5/0x250 do_shrink_slab+0x1f6/0x530 shrink_slab+0x32e/0x410 shrink_node+0x2a5/0xba0 balance_pgdat+0x4bd/0x8a0 kswapd+0x35a/0x800 kthread+0x1e9/0x210 ret_from_fork+0x3a/0x50 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(fs_reclaim); lock(&delayed_node->mutex); lock(fs_reclaim); lock(&delayed_node->mutex); *** DEADLOCK *** 3 locks held by kswapd0/1133: #0: ffffffff8fc5f860 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x5/0x30 #1: ffffffff8fc380d8 (shrinker_rwsem){++++}, at: shrink_slab+0x1e8/0x410 #2: ffff8881e0e6c0e8 (&type->s_umount_key#42){++++}, at: trylock_super+0x1b/0x70 stack backtrace: CPU: 2 PID: 1133 Comm: kswapd0 Not tainted 5.6.0-c6f0579d496a+ #53 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 Call Trace: dump_stack+0xc1/0x11a print_circular_bug.isra.38.cold.57+0x145/0x14a check_noncircular+0x2a9/0x2f0 ? print_circular_bug.isra.38+0x130/0x130 ? stack_trace_consume_entry+0x90/0x90 ? save_trace+0x3cc/0x420 __lock_acquire+0x197e/0x2550 ? btrfs_inode_clear_file_extent_range+0x9b/0xb0 ? register_lock_class+0x960/0x960 lock_acquire+0x103/0x220 ? __btrfs_release_delayed_node+0x7c/0x5b0 __mutex_lock+0x13d/0xce0 ? __btrfs_release_delayed_node+0x7c/0x5b0 ? __asan_loadN+0xf/0x20 ? pvclock_clocksource_read+0xeb/0x190 ? __btrfs_release_delayed_node+0x7c/0x5b0 ? mutex_lock_io_nested+0xc20/0xc20 ? __kasan_check_read+0x11/0x20 ? check_chain_key+0x1e6/0x2e0 mutex_lock_nested+0x1b/0x20 ? mutex_lock_nested+0x1b/0x20 __btrfs_release_delayed_node+0x7c/0x5b0 btrfs_remove_delayed_node+0x49/0x50 btrfs_evict_inode+0x6fc/0x900 ? btrfs_setattr+0x840/0x840 ? do_raw_spin_unlock+0xa8/0x140 evict+0x19a/0x2c0 dispose_list+0xa0/0xe0 prune_icache_sb+0xbd/0xf0 ? invalidate_inodes+0x310/0x310 super_cache_scan+0x1b5/0x250 do_shrink_slab+0x1f6/0x530 shrink_slab+0x32e/0x410 ? do_shrink_slab+0x530/0x530 ? do_shrink_slab+0x530/0x530 ? __kasan_check_read+0x11/0x20 ? mem_cgroup_protected+0x13d/0x260 shrink_node+0x2a5/0xba0 balance_pgdat+0x4bd/0x8a0 ? mem_cgroup_shrink_node+0x490/0x490 ? _raw_spin_unlock_irq+0x27/0x40 ? finish_task_switch+0xce/0x390 ? rcu_read_lock_bh_held+0xb0/0xb0 kswapd+0x35a/0x800 ? _raw_spin_unlock_irqrestore+0x4c/0x60 ? balance_pgdat+0x8a0/0x8a0 ? finish_wait+0x110/0x110 ? __kasan_check_read+0x11/0x20 ? __kthread_parkme+0xc6/0xe0 ? balance_pgdat+0x8a0/0x8a0 kthread+0x1e9/0x210 ? kthread_create_worker_on_cpu+0xc0/0xc0 ret_from_fork+0x3a/0x50 This is because we hold that delayed node's mutex while doing tree operations. Fix this by just wrapping the searches in nofs. Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- fs/btrfs/delayed-inode.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)